Tuning a 102"

[The DB]

102" is closer to the 10 meter ham band than the 11 meter cb band. To be resonant on the CB band you need to use a 6" riser, or you can settle for a spring as well. Of course this will vary from setup to setup.

The 102" whip is wide banded enough that if it were tuned for the 23 channel radios, it would easily cover the newer 17 channels easily as well. Even with all 40 channels the cb band is very narrow, about half a Mhz wide, and most antennas that haven't been shortened to an obscenely short length should easily cover the band. The 102" whip is wide banded enough to cover the CB band when tuned to 10 meters or vice versa if you want an antenna that can do both.


The DB

 

[Brake Weight]

A 108" is available from one maker. My 102" nets a 1.6-1.7 to 1, channels 1-40 without a spring. Radio reads less.

 

[binrat]

For me, my install measures 109". I got coverage on lower 10 metres as well as just shy of 12.

 

[The DB]

A 108" is available from one maker.

I know MFJ sells 108" whips, not sure about anyone else. You shouldn't need a spring or riser in this case.


The DB

 

[The DB]

For me, my install measures 109". I got coverage on lower 10 metres as well as just shy of 12.

Yep, that is the antenna at work. I have seem some actually give full 10/11/12 meter coverage with 1.5:1 the highest SWR on any of the ham/cb bands.


The DB

 

[KM3F]

Here is a cheaper way of getting good results.
A Noise Bridge is often advertised used at about $30 for a PALAMAR unit or about $70 from MFJ.
Build a """"flat""" 50 ohm load as a reference piece of test gear.
Connect the Bridge to your receiver and the antenna port to the flat load.
Adjust both dials for min to no noise in the receiver.
Look at the two dials.
The R dial should read 50, the Z dial close to zero or center position indicating the load is flat, 50 ohms and purely resistive with no reactance either way, Z C/L.
Then sub the antenna for your Load and play with the dials for lowest noise in the receiver.
What you read on the dials tells you what the antenna impedance is likely to be.
You make adjustment to the set up until you get as close as you can get to 50 and center the dial for the noise null.
Center dial is the point between capacitive reactance and inductive reactance.
Afterwards put your SWR meter in line as you normally would do and check what it says as a cross reference but keep in mind insturment accuracy and tolerences.
The flat load test of the SWR meter should also show no reflected power in an actual power test. This is why the flat load is a reference for you and testing to see who's 'lying' at times and who is out of adjustment or faulty..
For a lot less than $260 you can accomplish the same thing and learn a great deal.
The Bridge puts out wide band noise into a bridge circuit whos 'null' is at the impedeance the antenna port sees.
Never put transmitt power from the radio into the noise bridge or it burns it out.
This method tells you essentially the same thing as a 259 but a different way and cheaper..
Good luck.

 

[W5LZ]

There are several ways of going about that, they all work to some extent. The 'catch' to all of them is that you have to know the device's capabilities and how to use it. A noise bridge, grid-dip oscillator, or a light bulb can get you into the ball park. From there it's a matter of thinking the process through and making the required changes indicated. That 'thinking it through' is the part that fouls up most people. Not that they can't think, but that they don't have the knowledge of what's going on (or can go on). That's a lot like a 'rubic's cube', solvable, just very aggravating!
Have fun.
- 'Doc